Help with weld rotation?

Ok I made a weld script I welded two parts then I tried to rotate a part with a different script without moving the other when I did so it did rotate but also moved it in the sky the parts are unanchored this is my code. Can you help what wrong?

local rotation = -- a number that i want to rotate
local weld = --;-; The weld
weld.C0 = CFrame.fromEulerAnglesXYZ(0, rotation, 0);